
Preheat oven to 400ºF.
Place cauliflower, broccoli, and garlic cloves on a baking sheet. Drizzle 3 tablespoons of olive oil on top and toss so that the veggies are fully coated.
Roast veggies at 400ºF for about 20 minutes, or until the broccoli begins to brown.
While the veggies are roasting, sauté the yellow onion in about 1 tablespoon of olive oil with a pinch of salt. Once they are translucent, pour in the vegetable broth and let simmer for a few minutes.
Transfer all of the ingredients to a high-speed blender (including the cheese). If desired, set aside a couple roasted florets for topping.
Blend for about a minute, pureeing the vegetables and turning the mixture into a creamy soup.